The present invention generally relates to the field of thin film thickness mapping, and more specifically relates to a method for measuring thickness of textured polycrystalline thin films or coatings.
There is a great commercial need for stringent thickness control of crystalline plating, films, and coatings. The performance of many electronic devices is critically dependent on the film thickness. Significant manufacturing cost reductions and improvements in quality and reliability can be achieved by insuring that the applied film thickness is within the acceptance limits for a specific application.
X-ray diffraction (XRD) techniques enable measurement of the thickness of thin films in a non-destructive, non-contact, and quantitative manner.
Conventional XRD-based film thickness measurement analyzes the attenuation of the diffraction intensity, by comparing the integrated intensity of the incident x-ray with the integrated intensity of the x-ray diffracted from the films themselves or from the films and the substrate, according to the kinematical expression of the integrated diffraction intensity.
J. Chaudhuri (J. Chaudhuri and F. Hashmi, xe2x80x9cDetermination of thickness of multiple layer thin films by and x-ray diffraction technique,xe2x80x9d J. Appl. Phys. 76 (7), (1994), pp. 4454-4456) proposed a technique for determining thickness of multiple heteroepitaxial films deposited on a single crystal substrate, based on the integrated intensity reflected on rocking curve of each film and substrate. Chaudhuri corrects the kinematical expression of the integrated diffraction intensity, by applying the primary and secondary extinction of diffracted x-rays, according to the mosaic crystal model established by C. G. Darwin in Phil. Mag., vol. 27, pp. 315 and 657 (1914) and vol. 43, pg. 800 (1922). The block thickness of such mosaic crystal model was assumed a priori, and the constant referring to block tilts is determined through calibration using a single film with known thickness.
However, the technique disclosed by Chaudhuri applies only to heteroepitaxial films, which are characterized by single crystal-like texture, and is not suitable for determining thickness of a textured polycrystalline film or stacks of films, where the crystallographic texture varies widely and impacts the diffraction intensities differently.
Ruud (C. O. Ruud, M. E. Jackobs, xe2x80x9cMethod and apparatus for in-process analysis of polycrystalline films and coatings by x-ray diffraction,xe2x80x9d U.S. Pat. No. 5,414,747, May 9, 1995) proposed to use multiple position sensitive detectors to register multiple diffraction peaks simultaneously. Specifically, Ruud uses the diffraction intensity of one or more diffraction peaks from the substrate to calculate the thickness of the coating, presumably according to the absorption equations. However, Ruud does not suggest or teach elimination of crystallographic texture effects from the measurements of diffraction peak intensity.
It is therefore an object of the present invention to provide a method for determining thickness of textured polycrystalline thin films, by correcting the diffraction intensity measurement to eliminate crystallographic texture impacts therefrom.
It is another object of the present invention to provide a film thickness mapping system, which rapidly and automatically collects and processes diffraction data for determining thickness of textured polycrystalline thin films.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.
One aspect of the present invent relates to a method for determining film thickness of a textured polycrystalline thin film of unknown thickness, comprising the steps of:
(a) providing a plurality of sample films comprising textured polycrystalline materials and having known film thickness;
(b) collecting multiple incomplete pole figures of a sample film, by:
(i) irradiating a measurement point on such sample film with radiation energy from a radiation source;
(ii) detecting the radiation energy diffracted from such sample film at a detection locus, wherein the detection locus is in sufficient proximity to the measurement point for capturing a plurality of diffraction arcs within a single data capture frame; and
(iii) generating a diffraction image containing multiple incomplete pole figures;
(c) calculating complete pole densities for a particular set of diffracting planes of such sample film, based on the incomplete pole figures collected on the diffraction image;
(d) obtaining values of diffraction intensities for the particular set of diffracting planes from the diffraction image;
(e) correcting the values of diffraction intensities to eliminate crystallographic texture impacts therefrom, by using the pole densities calculated in step (c);
(f) integrating the corrected values of diffraction intensities for the particular crystallographic orientation to form a corrected and integrated diffraction intensity for the particular set of diffracting planes of such sample film;
(g) repeating steps (b) to (f) for each sample film, while fixing the instrumental set up during data acquisition for all the sample films, so as to obtain a corrected and integrated diffraction intensity of the particular set of diffracting planes for each sample film;
(h) constructing a calibration curve, which correlates the corrected and integrated diffraction intensities in step (g) obtained for the sample films with the respective known film thickness of such sample films;
(i) obtaining a corrected and integrated diffraction intensity for the particular set of diffracting planes of the textured polycrystalline thin film of unknown thickness; and
(j) mapping the film thickness of the textured polycrystalline thin film on the calibration curve, based on the corrected and integrated diffraction intensity obtained for such textured polycrystalline thin film.
The phase xe2x80x9cthin filmxe2x80x9d as used herein refers to a film having a thickness within the range of from about 0.1 nm to about 2000 nm.
Another aspect of the present invention relates to a thickness mapping system for determining film thickness of a textured polycrystalline thin film, comprising:
a sample comprising the textured polycrystalline thin film deposited on a generally planar substrate, said sample defining an associated sample plane;
a radiation source for directing radiation energy to a measurement point on the sample;
a 2-dimensional area detector that registers radiation energy diffracted from the sample at the measurement point, with the radiation source and the 2-dimensional area detector being in a fixed spatial relationship to one another and sufficiently proximate to the measurement point to capture a plurality of diffraction arcs within a single data capture frame of the area detector;
a sample motion assembly for translating the sample in the sample plane; and
a computer-based film thickness processor, construed and arranged to collect and process diffraction data for determining film thickness of the textured polycrystalline thin film.